Image pickup apparatus and radiatioin image pickup apparatus

ABSTRACT

To improve a sensor resetting method and thereby implement a high rate at which a moving image is read, the invention provides an image pickup apparatus and a radiation image pickup apparatus including: a plurality of pixels arranged on a substrate in row and column directions, each pixel having a conversion element and a transfer switching element; a drive wiring connected to a plurality of the transfer switching elements in the row direction; and a conversion element wiring connected to a plurality of the conversion elements in the row direction, wherein a reset switching element is disposed between the conversion element wiring and a reset wiring for supplying a reset voltage for resetting the conversion element, and a bias switching element is disposed between the conversion element wiring and a bias wiring for supplying a bias voltage for operating the conversion element.

RELATED APPLICATIONS

This application is a divisional of A.N. 11/229,630, filed Sep. 20,2005, claims benefit of that application under 35 U.S.C. § 120, claimsbenefit under 35 U.S.C. § 119 of Japanese patent application no.286995/2004, filed Sep. 30, 2004, and incorporates by reference theentire disclosure of both of the mentioned prior applications.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image pickup apparatus whichconverts an image to an electrical signal, and more particularly to aradiation image pickup apparatus which detects radiation such as anX-ray, γ-ray or the like. The radiation image pickup apparatus isapplied to a medical image diagnosis apparatus, a non-destructiveexamination apparatus, an analysis apparatus using radiation, and thelike.

2. Related Background Art

Conventionally, imaging methods used in medical image diagnosis areclassified into general imaging for obtaining a still image andradiographic imaging for obtaining a moving image. Each of the imagingmethods and imaging apparatuses may be selected as required.

The methods of general imaging for obtaining a still image includes oneof exposing a film of a screen-film system (hereinafter referred to asan S/F system) comprised of a combination of a fluorescent plate and afilm, developing the film, and then fixing the resultant image. Anothergeneral method is computed radiography (CR) in which a radiographicimage is first recorded as a latent image on a photostimulable phosphor,and then the photostimulable phosphor is scanned with a laser beam andoutput optical information is read using a sensor (computed radiography,referred to below as CR). However, a problem in both the methods is thatthey require complicated work flow to obtain a radiographic image.Another problem is that a digital radiographic image can be obtainedindirectly via processing in both the methods, but cannot be obtained inreal time. Furthermore, under the medical environments of such digitalimaging apparatuses as CT and MRI used in medical image diagnosis, itseems difficult to adequately adjust both the methods to these digitalimaging apparatuses.

In the radiography for obtaining a moving image, an image intensifier(referred to below as an I.I) using an electron tube is mainly used.However, this method requires a large-scale apparatus because of usingthe electron tube. Also, the field of view or the detection area is notlarge enough to be used in the field of medical image diagnosis, and itis desirable to enlarge the detection area. Furthermore, an obtainedmoving image includes a large amount of crosstalk arising from aspecific structure of the apparatus, and it is desirable to reducecrosstalk to obtain a clearer image.

On the other hand, as the liquid crystal TFT technology and informationinfrastructure have advanced in recent years, there has been proposed inJapanese Patent Application Laid-Open No. 08-116044 etc., a flat paneldetector (referred to below as a FPD) comprised of a combination of: asensor array composed of a photoelectric conversion element and aswitching TFT each using non-single crystalline silicon, e.g., amorphoussilicon (referred to below as a-Si); and a phosphor for convertingradiation to visible light. The FPD is expected to make it possible tocreate large-area radiographic images in a digital form.

The FPD is capable of reading a radiographic image and displaying theimage on a display in real time. Another advantage is that a digitalimage data can be obtained directly, so data can be easily stored,processed, and transferred. Although characteristics such as sensitivitydepend on imaging conditions, the characteristics are generally similarto or better than the characteristics obtained in the conventional S/For CR imaging techniques.

FIG. 12 shows a schematic equivalent circuit diagram of the FPD.

In FIG. 12, reference numeral 101 denotes a conversion element using aphotoelectric conversion element, 102 denotes a transfer switchingelement composed of a TFT, 103 denotes a drive wiring connected to thegate electrode of the transfer switching element 102 to supply a drivesignal to a transfer switching element, 104 denotes a signal wiring fortransmitting a signal transferred from the conversion element 101 viathe transfer switching element 102, 105 denotes a sensor bias wiringconnected to plural conversion elements 101 to supply a bias foroperating the conversion element 101, 106 denotes a signal processingcircuit for processing signals transmitted via the signal wiring 104,107 denotes a drive circuit for supplying a drive signal for driving thetransfer switching element 102, and 108 denotes an A/D converter.

Radiation, such as an X-ray, is incident on the conversion element 101from the upper section of the drawing, and the incident radiation isconverted in wavelength into light sensible by the conversion element101 by a wavelength converter (not shown), such as a phosphor. Theresultant converted light is then converted to an electric charge by theconversion element 101 being a photoelectric conversion element andstored in the conversion element 101. Thereafter, the drive circuit 107supplies a drive signal to the transfer switching element 102 via thedrive wiring 103 so as to transfer the electric charge stored in theconversion element 101 to the signal wiring 104. The transferredelectric charge is processed by the signal processing circuit 106 andthen converted by the A/D converter 108 from analog form into digitalform. The resultant digital signal is output as an image signal.

A typical element structure of the FPD has been described above.Especially, as for the conversion element, photoelectric conversionelements such as a PIN-type photodiode or MIS-type photo sensor havebeen proposed.

FIG. 13 is a schematic plan view showing one pixel in which a MIS-typephoto sensor is used as the photoelectric conversion element being aconversion element.

In FIG. 13, reference numeral 201 denotes a MIS-type photo sensor, 202denotes a transfer switching element composed of a TFT, 203 denotes adrive wiring, 204 denotes a signal wiring, 205 denotes a sensor biaswiring, 211 denotes a gate electrode of a transfer switching elementcomposed of a TFT, 212 denotes source and drain electrodes of thetransfer switching element, and 213 denotes a contact hole.

FIG. 14 is a cross-sectional view of one pixel having arranged thereinvarious elements shown in FIG. 13.

In FIG. 14, reference numeral 301 denotes an insulating substrate suchas a glass substrate, 302 denotes a drive wiring, 303 denotes a lowerelectrode of the conversion element being an MIS-type photo sensor, 304denotes the gate electrode of the transfer switching element, 305denotes a gate insulating film, 306 denotes a semiconductor layer beingan intrinsic a-Si film, 307 denotes an impurity semiconductor layer, 308denotes a sensor bias wiring, 309 denotes the source and drainelectrodes of the transfer switching element, 310 denotes a signalwiring, 320 denotes a protective film, 321 denotes a passivation layercomposed of an organic resin etc., and 322 denotes a phosphor layer.

As can be seen from FIGS. 13 and 14, the MIS-type photo sensor and thetransfer switching element composed of a TFT have the same layerstructure, and thus they can be produced using a simple productionmethod which allows a high production yield and low production cost.Furthermore, the above-described FPD adequately satisfies variouscharacteristics, including sensitivity, and thus it has come to be usedin general imaging applications instead of conventional S/F method andCR method apparatuses.

However, although the FPD has the advantage that a fully digitallarge-area image can be obtained and the FPD has come to be used widelyin general imaging, the FPD according to the conventional technologydoes not have a high enough reading rate needed in radiographic imaging.

FIG. 15 is an equivalent circuit diagram of a one-bit portion of an FPDusing a MIS-type photo sensor as the conversion element.

In FIG. 15, reference character C₁ denotes a total equivalentcapacitance of the conversion element being a MIS-type photo sensor, C₂denotes a parasitic capacitance created in the signal wiring, Vs denotesa sensor bias voltage for operating the conversion element, Vr denotes asensor reset voltage for resetting the conversion element, SW₁ denotes aswitch for selecting Vs or Vr applied to the conversion element being aMIS-type photo sensor, SW₂ denotes a switch for turning on/off thetransfer switching element, SW₃ denotes a switch for resetting thesignal wiring, and Vout denotes an output voltage.

The sensor bias voltage Vs is applied via the SW₁ to the MIS-type photosensor such that the semiconductor layer of the MIS-type photo sensor isdepleted. In this state, if light from the wavelength converter such asa phosphor is incident on the semiconductor layer, a positive electriccharge blocked by the impurity semiconductor layer is accumulated intothe semiconductor layer, and a voltage difference Vt is generated.Thereafter, when the on-voltage is applied to the transfer switchingelement via the SW₂, the voltage Vout is output. The output Vout is readby a reading circuit (not shown). After that, the signal wiring is resetby the SW₃, and reading is performed sequentially by repeating the abovedescribed steps for each row.

By sequentially turning on transfer switching elements on a per-rowbasis according to the drive method described above, reading of oneframe of image signals is completed. Thereafter, all the conversionelements being MIS-type photo sensors are reset as a whole by applyingthe reset voltage Vr to them via the SW₁, and the bias voltage Vs isagain applied, thereby causing the charge accumulation to start in theimage reading operation.

For example, when the FPD has pixels with a size of 160 μm arranged in apixel area with a size of 43 cm×43 cm, the total equivalent capacitanceC₁ of the MIS-type photo sensor is about 1 pf and the parasiticcapacitance C₂ is about 50 pf. In such an FPD, when the charge istransferred, about 2% of the charge remains in the capacitor C₁ withoutbeing transferred because of the charge sharing effect. Thus, to obtaina high-quality image, it is necessary to perform the reset operationdescribed above at the time of imaging operation.

More specifically, the reset operation is performed all at once for theconversion elements, and stabilizing time of the sensor voltage etc.should be taken into consideration, so the reset operation needs tenmsec or a few ten msec for each frame, which naturally depends on thereset condition. In other words, when it is desired to take aradiographic image at a rate of 30 frames per second (referred to belowas 30 FPS) or at a higher rate, it is required to perform reading andresetting on all lines of one frame within a period of 33 msec (30 FPS).

FIG. 16 is a schematic diagram for explaining the drive method.

In FIG. 16, reference character T₁ denotes a period of time needed toread one line, T₂ denotes a period of time needed to read all lines, T₃denotes a reset time, and T denotes a period of time needed to performthe entire process on one frame.

In the case in which it takes less than 33 msec (T) to perform theentire process on one frame as described above, if the reset time T₃ isequal to 15 msec, then T₂ becomes 18 msec. Therefore, if there are 1500lines to be read, the period of time T₁ available for reading one linebecomes 12 μsec. If a radiation exposure time, that is, a sensoraccumulation time is taken into account, the reading period T₁ isfurther limited. Thus, it becomes necessary to increase the transfercapacity of the transfer switching element. However, to increase thetransfer capacity of the transfer switching element, it is necessary toincrease the size of the transfer switching element at the cost of theaperture ratio, which causes various problems such as a reduction insensitivity, degradation in image quality, and an increase in the amountof radiation.

That is, a trade-off is needed between the high image quality and thehigh rate at which the FPD is driven to obtain a moving image. In otherwords, at present, it is impossible to achieve a high-rate moving imagehaving high quality.

An example in which a MIS-type photo sensor is used as the conversionelement has been described above. However, the same problem caused bythe reset time in obtaining a moving image applies to a PIN-type photodiode.

SUMMARY OF THE INVENTION

An object of the present invention is to improve a method of resetting aconversion element so as to implement a high rate at which a movingimage is read.

To solve the above problem, according to one aspect of the presentinvention, there is provided an image pickup apparatus according to thepresent invention comprising: a plurality of pixels arranged on asubstrate in row and column directions, each pixel having a conversionelement and a transfer switching element; a drive wiring connected tothe plurality of transfer switching elements in the row direction; and awiring connected to the plurality of conversion elements in the rowdirection, wherein a reset switching element is arranged between thewiring and a reset wiring for supplying a reset voltage for resettingthe conversion element, and a bias switching element is arranged betweenthe wiring and a bias wiring for supplying a bias voltage for operatingthe conversion element.

According to another aspect of the present invention, there is provideda radiation image pickup apparatus comprising: a plurality of pixelsarranged on a substrate in row and column directions, each having aconversion element for converting radiation to an electrical signal anda transfer switching element for transferring the electrical signal; adrive wiring connected to the plurality of transfer switching elementsin the row direction; and a conversion element wiring connected to theplurality of conversion elements in the row direction, wherein a resetswitching element is disposed between the wiring and a reset wiring forsupplying a reset voltage for resetting the conversion element, and abias switching element is disposed between the wiring and a bias wiringfor supplying a bias voltage for operating the conversion element.

According to the present invention, in the pixels arrangedtwo-dimensionally, it becomes possible that, after transferring a chargeon a per-line basis, the conversion element is reset on a per-line basisto be restored to the charge accumulation state. Accordingly, the resettime taken to reset the conversion elements all at once in theconventional method is shortened to achieve a high-rate drive of movingimage. Thus the moving image drive at a rate of 30 FPS or at a higherrate can be realized easily and at low cost without degrading the imagequality.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a schematic equivalent circuit diagram of 4×2 pixels accordingto Embodiment 1 of the present invention;

FIG. 2 is a diagram for explaining a drive timing according toEmbodiment 1 of the present invention;

FIG. 3 is a diagram for explaining the operation on one frame accordingto Embodiment 1 of the present invention;

FIG. 4 is a schematic plan view showing one pixel according toEmbodiment 1 of the present invention;

FIG. 5 is a schematic cross-sectional view showing one pixel along theline 5-5 in FIG. 4 of the present invention;

FIG. 6 is a plan view showing a variation of the panel according toEmbodiment 1 of the present invention;

FIG. 7 is a schematic equivalent circuit diagram of 3×3 pixels accordingto Embodiment 2 of the present invention;

FIG. 8 is a diagram for explaining a drive timing according toEmbodiment 2 of the present invention;

FIG. 9 is a schematic equivalent circuit diagram of 3×3 pixels accordingto Embodiment 3 of the present invention;

FIG. 10 is a schematic cross-sectional view showing one pixel accordingto Embodiment 3 of the present invention;

FIG. 11 is a view showing a radiation detecting system according to thepresent invention;

FIG. 12 is a schematic equivalent circuit diagram of a conventionalradiation image pickup apparatus;

FIG. 13 is a schematic plan view showing one pixel when a MIS-type photosensor is used as a conventional conversion element;

FIG. 14 is a cross-sectional view having schematically disposed thereineach element within one pixel shown in FIG. 13;

FIG. 15 is an equivalent circuit diagram of a one-bit portion of aradiation image pickup apparatus using a conventional MIS-type photosensor; and

FIG. 16 is a schematic diagram for explaining the drive method of theconventional radiation image pickup apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described withreference to the accompanying drawings. Embodiments of the presentinvention will be described below by way of examples in which thepresent invention is applied to a radiation image pickup apparatus.However, the embodiments 1, 2 and 4 can also be applied to an imagepickup apparatus for converting an optical image other than radiation toan electrical signal.

Firstly the summary of the read method of a radiation image pickupapparatus of the present invention will be described. Pixels composed ofa conversion element and transfer switching element are arrangedtwo-dimensionally in rows and columns; the transfer switching element isoperated on a per-row basis, and a signal is read on a per-column basis.A drive wiring connected to plural transfer switching elements for eachrow, and a sensor drive wiring, connected to plural conversion elements,for supplying a bias for operating the conversion element are arrangedparallel to each other. In addition, there are provided second switchingelements connected to the sensor drive wirings of the first, second andsubsequent rows. After a signal is transferred by the transfer switchingelement of the first row, the second switching element is operated usinga drive signal for driving the transfer switching elements of the secondand subsequent rows, and a reset voltage for resetting the conversionelement is supplied to the conversion element of the first row.Thereafter, the conversion element again receives a bias voltage to berestored to the signal accumulation state. Consequently, the transfer,resetting and accumulating operations are cyclically performed on aper-row basis to achieve a moving image drive.

Embodiment 1

In this first embodiment, there is described a radiation image pickupapparatus using a MIS-type photo sensor as a conversion element.

FIG. 1 is a schematic equivalent circuit diagram of 4×2 pixels accordingto the present embodiment. In FIG. 1, reference numeral 11 denotes aconversion element being a MIS-type photo sensor, 12 denotes a transferswitching element composed of a TFT, 13 denotes a drive wiring connectedto a gate electrode of the transfer switching element 12 for supplying adrive signal to the transfer switching element, 14 denotes a signalwiring for transmitting a signal transferred from the conversion element11 via the transfer switching element 12, 15 denotes a sensor drivewiring, connected to plural conversion elements 11, for supplying a biasfor operating the conversion element 11, 16 denotes a signal processingcircuit which processes a signal transmitted via the signal wiring 14,17 denotes a drive circuit which supplies drive signals for driving thetransfer switching element 12 etc., 18 denotes an A/D converter, 19denotes a bias wiring for supplying a bias voltage for operating theconversion element 11, 20 denotes a reset wiring for supplying a resetvoltage for resetting the conversion element 11, 21 denotes a resetswitching element, composed of a TFT, which connects the drive wiring 15and reset wiring 20, 22 denotes a first bias switching element composedof a TFT, disposed between the bias wiring and sensor drive wiring,which is turned on in response to a drive signal from the drive wiring13 of a previous row to thereby supply a bias voltage to the conversionelement 11, 23 denotes a second bias switching element composed of aTFT, disposed between the bias wiring and sensor drive wiring, which isturned on in response to a drive signal from the drive wiring 13 of anext row to thereby supply again a bias voltage to the conversionelement 11.

An X-ray is converted in wavelength into light sensible by theconversion element 11 by a wavelength converter such as a phosphor (notshown), and is incident on the conversion element 11 composed of aMIS-type photo sensor.

The incident light is converted to an electric charge by the conversionelement and accumulated in the conversion element 11.

Firstly a drive signal from the drive circuit 17 is supplied to a dummyline dubbed the 0^(th) stage in FIG. 1 to turn on the first biasswitching element 22 of the first row, whereby a sensor bias voltage Vsis applied to the sensor drive wiring 15. Then, a drive signal issupplied to the drive wiring 13 of the first row to turn on the transferswitching element 12 of the first row, whereby an accumulated charge isread. At this time, since the gate electrode of the first bias switchingelement 22 of the second row is connected to the drive wiring of thefirst row, the sensor bias voltage Vs is supplied to the sensor drivewiring 15 of the second row via the first bias switching element 22 ofthe second row.

Thereafter, a drive signal is supplied to the drive wiring 13 of thesecond row to turn on the transfer switching element 12. At this time,since the gate electrode of the reset switching element 21 of the firstrow is connected to the drive wiring 13 of the second row, the resetswitching element 21 of the first row is turned on. Thus a reset voltageVr is supplied to the conversion element 11 of the first row to resetit. Then, when the transfer of the second row is completed and a drivesignal is supplied to the signal wiring 14 of the second row such thatthe transfer switching element 12 of the second row is turned off, thereset switching element 21 of the first row is turned off, wherebyresetting of the conversion element 11 of the first row is completed.

Then a drive signal is supplied to the drive wiring 13 of the third rowto turn on the transfer switching element 12 of the third row. At thistime, since the gate electrode of the second bias switching element 23of the first row is connected to the signal wiring 13 of the third row,the second bias switching element 23 of the first row is turned on,whereby the conversion element 11 of the first row receives the sensorbias voltage Vs to become an accumulation state.

The above described charge reading, resetting and accumulatingoperations are cyclically performed on a per-row basis.

FIG. 2 is a diagram for explaining the drive timing.

FIG. 3 is a diagram for explaining the operation on one frame.

In FIG. 3, reference character S₁ denotes a period of time needed toperform reading etc. on one line, S₂ denotes a period of time needed toperform resetting etc. on one line, S₃ denotes a period of time neededto perform transfer, resetting, etc. on one line, S₄ denotes a period oftime needed for the sensor to perform accumulation on one line, and Sdenotes a period of time needed to perform the entire process on oneframe.

In contrast to the conventional method, according to the presentembodiment, the reading, resetting and accumulating operations can beperformed on a per-row basis. Therefore, the entire drive can beperformed in a period of time obtained by combining all the read timeperiods. Specifically, simultaneously with performing reading on onerow, the resetting of the conversion elements of that row on whichreading has been completed is performed. Accordingly, the moving imagedrive at a rate of 30 FPS or at a higher rate can be realized withoutdegrading image quality.

FIG. 4 is a schematic plan view showing one pixel according to thepresent embodiment.

In FIG. 4, the same reference numerals are applied to partscorresponding to FIG. 1.

FIG. 5 is a schematic cross-sectional view along the line 5-5 in FIG. 4;

In FIG. 5, reference numeral 31 denotes an insulating substrate, 32denotes a gate electrode of the transfer switching element, 33 denotes agate insulating layer (SiN), 34 denotes an intrinsic semiconductor layer(a-Si), 35 denotes an impurity semiconductor layer (n+) having an ohmiccontact function, 36 denotes a source/drain electrode, 37 denotes afirst protective layer, 38 denotes an interlayer insulator being aflattening film, 39 denotes a lower electrode of the MIS-type photosensor, 40 denotes an insulating layer (SiN) of the MIS-type photosensor, 41 denotes an intrinsic semiconductor layer (a-Si) of theMIS-type photo sensor, 42 denotes an impurity semiconductor layer (n+)of the MIS-type photo sensor having a carrier blocking function, 43denotes the sensor drive wiring of the MIS-type photo sensor, 44 denotesa second protective layer, 45 denotes an adhesive layer, and 46 denotesa phosphor layer (CsI, GOS). In the present embodiment, switchingelements such as a TFT, and conversion elements such as a photoelectricconversion element are each composed of a thin layer of the amorphoussilicon family.

According to the present embodiment, the sensor drive wiring 43 of theMIS-type photo sensor is formed in a crossed manner relative to thesignal wiring connected to the source/drain electrode 36 via the firstprotective layer 37, the interlayer insulator 38, the insulating layerof the MIS-type photo sensor 40 and the intrinsic semiconductor layer ofthe MIS-type photo sensor 41. Therefore, the increase of parasiticcapacitance of the signal wiring can be neglected.

FIG. 6 is a plan view showing a variation of the panel according toEmbodiment 1.

The reset switching element, first bias switching element and secondbias switching element composed of a TFT are each connected to theconversion element of each row. Accordingly, needless to say, it isneeded for the ON resistance of each switching element to be small in adrive performed at a high rate. Meanwhile, as shown in FIG. 6, when asensor panel substrate 10 is driven from the both sides and read fromthe both sides, the parasitic capacitance of the reset switchingelement, first bias switching element and second bias switching elementis halved, whereby the drive can be easily performed.

In the present embodiment, there was described an example in which aMIS-type photo sensor is used as the conversion element. However, ofcourse, the present embodiment is similarly applicable to a case inwhich a PIN-type photo diode is used, and the drive can be performed ata high rate. In other words, when a resetting is needed in the operationof a conversion element, the present invention is effectivelyapplicable.

Embodiment 2

In this second embodiment, there is described a radiation image pickupapparatus using a MIS-type photo sensor as a conversion element and aPoly-Si TFT as a switching element.

FIG. 7 is a schematic equivalent circuit diagram of 3×3 pixels accordingto the present embodiment.

In FIG. 7, reference numeral 11 denotes a conversion element being aMIS-type photo sensor, 12 denotes a transfer switching element composedof a Poly-Si TFT, 13 denotes a drive wiring, connected to a gateelectrode of the transfer switching element 12, for supplying a drivesignal to the transfer switching element 12, 14 denotes a signal wiringfor transmitting a signal transferred from the conversion element 11 viathe transfer switching element 12, 15 denotes a sensor drive wiring,connected to plural conversion elements 11, for supplying a bias foroperating the conversion element 11, 16 denotes a signal processingcircuit which processes a signal transmitted via the signal wiring 14,17 denotes a drive circuit which supplies drive signals for driving thetransfer switching element 12 etc., 19 denotes a bias wiring forsupplying a bias voltage for operating the conversion element 11, 20denotes a reset wiring for supplying a reset voltage for resetting theconversion element 11, 24 denotes a reset switching element (composed ofa N-channel TFT in the present embodiment) which connects the drivewiring 15 and reset wiring 20, and 25 denotes a bias switching element(composed of a P-channel TFT in the present embodiment), disposedbetween the bias wiring and sensor drive wiring, for supplying a biasvoltage to the conversion element 11.

An X-ray is converted in wavelength into light sensible by theconversion element 11 by a wavelength converter such as a phosphor (notshown), and is incident on the conversion element 11 composed of aMIS-type photo sensor. The incident light is converted from optical formto electric form by the conversion element 11 and accumulated in theconversion element 11.

Firstly a drive signal from the drive circuit 17 is supplied to thedrive wiring 13 of the first row to turn on the transfer switchingelement 12, whereby the electric charge accumulated in the conversionelement 11 is read. Hereafter, a drive signal is supplied to the drivewiring 13 of the second row to turn on the transfer switching element12. At this time, since the gate electrode of the reset switchingelement 24 of the first row is connected to the drive wiring 13 of thesecond row, the reset switching element 24 of the first row is turnedon, whereby a reset voltage Vr is supplied to the conversion element 11of the first row to be reset. At this time, the sensor bias switchingelement 25 is turned off.

Thereafter, a drive signal is supplied to the drive wiring 13 of thesecond row such that the transfer switching element 12 of the second rowis turned off, and the transfer switching element 12 of the second rowis turned off. At this time, the reset switching element 24 whose gateelectrode is connected to the drive wiring 13 of the second row isturned off, and the bias switching element 25 is turned on, whereby theconversion element 11 of the first row receives a bias voltage Vs tobecome an accumulation state.

The above described charge reading, resetting and accumulatingoperations are cyclically performed on a per-row basis.

FIG. 8 is a diagram for explaining a drive timing according to thepresent embodiment.

In contrast to the conventional method, according to the presentembodiment, the reading, resetting and accumulating operations can beperformed on a per-row basis. Therefore, the entire drive can beperformed in a period of time obtained by adding all the read timeperiods. Accordingly, the moving image drive at a rate of 30 FPS or at ahigher rate can be realized without degrading image quality. Also, byusing a N-channel TFT as the reset switching element and a P-channel TFTas the bias switching element, the moving image drive at a high rate canbe realized with a simple circuit configuration without increasing thesize of peripheral circuitry.

In the present embodiment, also, there was described an example in whicha MIS-type photo sensor is used as the conversion element. However, ofcourse, the present embodiment is similarly applicable to a case inwhich a PIN-type photo diode is used, and the drive can be performed ata high rate. In other words, when a resetting is needed in the operationof a conversion element, the present invention is effectivelyapplicable.

Embodiment 3

In this third embodiment, there is described a case in which the presentinvention is applied to a direct conversion technique for directlyconverting radiation to an electric charge, storing the obtainedelectric charge, and reading the electric charge using a transferswitching element.

FIG. 9 is a schematic equivalent circuit diagram of 3×3 pixels accordingto the present embodiment.

In FIG. 9, reference numeral 28 denotes a conversion element whichdirectly converts radiation to an electric charge, 27 denotes acapacitor which accumulates the electric charge from the conversionelement 28, 12 denotes a transfer switching element composed of a TFT,13 denotes a drive wiring, connected to the gate electrode of thetransfer switching element 12, for supplying a drive signal to thetransfer switching element 12, 14 denotes a signal wiring fortransmitting a signal transferred from the conversion element 28 via thetransfer switching element 12, 15 denotes a sensor drive wiring,connected to plural conversion elements 28, for supplying a bias foroperating the conversion element 28, 16 denotes a signal processingcircuit which processes a signal transmitted via the signal wiring 14,17 denotes a drive circuit which supplies drive signals for driving thetransfer switching element 12 etc., 19 denotes a bias wiring forsupplying a bias voltage for operating the conversion element 28, 20denotes a reset wiring for supplying a reset voltage for resetting theconversion element 28, 24 denotes a reset switching element whichconnects the drive wiring 15 and reset wiring 20, and 25 denotes a biasswitching element, disposed between the bias wiring and sensor drivewiring, for supplying a bias voltage to the conversion element 28.According to the present embodiment, the reset switching element 24 isan N-channel type TFT, and the bias switching element 25 is a P-channeltype TFT. The conversion element 28 is composed of amorphous selenium orGaAs.

An X-ray is incident on the conversion element 28. The incidentradiation is directly converted to an electric charge by the conversionelement 28 and accumulated in the capacitor 27.

Firstly a drive signal from the drive circuit 17 is supplied to thedrive wiring 13 of the first row to turn on the transfer switchingelement 12, whereby the electric charge accumulated in the conversionelement 28 is read. Hereafter, a drive signal is supplied to the drivewiring 13 of the second row to turn on the transfer switching element12. At this time, since the gate electrode of the reset switchingelement 24 of the first row is connected to the drive wiring 13 of thesecond row, the reset switching element 24 of the first row is turnedon, whereby a reset voltage Vr is supplied to the conversion element 28of the first row to be reset. At this time, the sensor bias switchingelement 25 is turned off.

Thereafter, a drive signal is supplied to the drive wiring 13 of thesecond row such that the transfer switching element 12 of the second rowis turned off, and the transfer switching element 12 of the second rowis turned off. At this time, the reset switching element 24 whose gateelectrode is connected to the drive wiring 13 of the second row isturned off, and the bias switching element 25 is turned on, whereby theconversion element 28 of the first row receives a sensor bias voltage Vsto become an accumulation state.

The above described charge reading, resetting and accumulatingoperations are cyclically performed on a per-row basis. The basic drivemethod is performed similarly to Embodiment 2.

FIG. 10 is a schematic cross-sectional view showing one pixel accordingto the present embodiment.

In FIG. 10, reference numeral 31 denotes an insulating substrate, 32denotes a gate electrode of the transfer switching element, 33 denotes agate insulating layer (SiN), 34 denotes an intrinsic semiconductor layer(a-Si), 35 denotes an impurity semiconductor layer (n+) having an ohmiccontact function, 36 denotes a source/drain electrode, 37 denotes afirst protective layer, 38 denotes an interlayer insulator being aflattening film, 39 denotes a lower electrode of the conversion element28, 51 denotes a semiconductor layer (a-Se in the present embodiment) ofthe conversion element 28, 52 denotes an upper electrode of theconversion element 28, 43 denotes the sensor drive wiring, 44 denotes asecond protective layer, and 53 denotes a lower electrode of thecapacitor.

In the present embodiment, a TFT formed of amorphous silicon is used asthe transfer switching element within a pixel, and a polysilicon TFT isused as the reset switching element and bias switching element. This isbecause it is important that the leak current is small within a pixel,and that the resistance is low outside a pixel. Needless to say, thesimilar effect can be achieved by using polysilicon TFTs connected inseries as the transfer switching element within a pixel so as to createan LDD structure.

The present embodiment also has the similar effect to that of Embodiment1 and Embodiment 2 described above; the reading, resetting andaccumulating operations can be performed on a per-row basis.Accordingly, the entire drive can be performed in a period of timeobtained by adding all the read time periods. Consequently, the movingimage drive at a rate of 30 FPS or at a higher rate can be realizedwithout degrading the image quality. Also, by using an N-channel TFT asthe reset switching element and a P-channel TFT as the bias switchingelement, the moving image drive at a high rate can be realized with asimple circuit configuration without increasing the size of peripheralcircuitry.

The radiation detecting apparatus according to the present invention isa two-dimensional flat panel detector having two-dimensionally disposedtherein pixels each composed of a conversion element and transferswitching element. In a two-dimensional flat panel detector in which ahigh-rate drive and a high image quality are desired, when a biasvoltage is applied thereto, a resetting operation is neededindependently of the type of conversion element. Therefore, theinventive method can be effectively applied.

In the present invention, the resetting operation is performed on aper-line basis. However, the resetting operation may be performed all atonce for several lines, or alternatively for odd-number or even-numberlines. The present invention does not exclude such other configurations:the similar effect can be achieved when the sensor drive wiring isarranged substantially parallel to the transfer switching element sothat the gate wiring drive is used.

Furthermore, the reset voltage or bias voltage from the drive circuitmay be applied to the conversion element on a per-row basis or on aper-several-row basis, which is substantially the same as the presentinvention.

According to each of the embodiments described above, the moving imagedrive at a rate of 30 FPS or at a higher rate can be realized easily andat low cost without degrading the image quality. By using an N-channelTFT or P-channel TFT being a polysilicon TFT, other than an amorphoussilicon TFT, as each of the reset switching elements, the moving imagedrive at a high rate can be realized with a simple circuit configurationwithout increasing the size of peripheral circuitry; cost reduction andhigh function can be achieved.

Embodiment 4

FIG. 11 is a view showing a radiation detecting system according to thisfourth embodiment.

The radiation detecting system is an example to which the radiationdetecting apparatus according to Embodiment 1, Embodiment 2 orEmbodiment 3 described above is applied.

An X-ray 6060 generated in an X-ray tube 6050 penetrates the chestregion 6062 of a patient or a subject 6061 and is incident onto aradiation detecting apparatus 6040 which takes a radiation image. Thisincident X-ray contains the information on the inside of the body of thepatient 6061. In response to the incidence of the X-ray, a scintillator(phosphor layer) of the radiation detecting apparatus 6040 emits light,and electrical data is obtained by converting the emitted light to anelectrical signal. This data is converted from analog to digital form,is subjected to image processing by an image processor 6070, and can beobserved on a display 6080 being display means in a control room.

This data can also be transferred to a remote place via transfer meanssuch as a telephone line 6090, and can thus be displayed on a display6081 in another place such as a doctor room, or saved in saving meanssuch as an optical disk. Accordingly, a doctor at a remote place canmake a diagnosis. Also, the data can be recorded on a film 6110 by afilm processor 6100.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the claims.

This application claims priority from Japanese Patent Application No.2004-286995 filed on Sep. 30, 2004, which is hereby incorporated byreference herein.

1. An image pickup apparatus comprising: a plurality of pixels arrangedon a substrate in row and column directions, each pixel having aconversion element including first and second electrodes and a transferswitching element connected to the first electrode of the conversionelement; a first wiring connected to the second electrodes of theplurality of the conversion elements arranged in the row direction; abias wiring for supplying a bias voltage for operating the conversionelements; a reset wiring for supplying a reset voltage for a reset ofthe conversion element; a bias switching element arranged between thebias wiring and the first wiring; and a reset switching element arrangedbetween the reset wiring and the first wiring, wherein at least the biasswitching element and the reset switching element comprise a poly-SiTFT.
 2. The image pickup apparatus according to claim 1, wherein thebias switching element comprises a first-type-channel TFT and the resetswitching element comprises a second-type-channel TFT, and thefirst-type channel is different from the second-type channel.
 3. Theimage pickup apparatus according to claim 2, wherein the bias switchingelement comprises a P-channel TFT and the reset switching elementcomprises an N-channel TFT.
 4. The image pickup apparatus according toclaim 1, wherein each of the transfer switching element and the resetswitching element have a gate electrode and a source or drain electrode,the gate electrodes of the plurality of transfer switching elements in arow direction are connected to a drive wiring, the source or drainelectrode of the reset switching element is connected to any one of thefirst wiring of a specific row and the reset wiring, and the gateelectrode of the reset switching element is connected to the drivewiring of a next row relative to the specific row.
 5. The image pickupapparatus according to claim 4, wherein the bias switching elementincludes a first bias switching element and a second bias switchingelement, each of the first and second bias switching elements have agate electrode and a source or drain electrode, the source or drainelectrodes of the first and second bias switching elements are eachconnected to any one of the first wiring and the bias wiring of aspecific row, the gate electrode of the first bias switching element isconnected to the drive wiring of a previous row relative to the specificrow, and the gate electrode of the second bias switching element isconnected to the drive wiring of the next row relative to the specificrow.
 6. The image pickup apparatus according to claim 5, wherein thegate electrode of the second bias switching element is connected to thedrive wiring of the next row relative to the drive wiring to which thegate electrode of the reset switching element of the specific row isconnected.
 7. The image pickup apparatus according to claim 4, whereinthe bias switching element has a gate electrode, a source or drainelectrode and a channel of which a conduction-type is different fromthat of a channel of the reset switching element, the source or drainelectrode is connected to any one of the conversion element wiring andthe bias wiring of a specific row, and the gate electrode is connectedto the drive wiring to which the gate electrode of the reset switchingelement is connected.
 8. The image pickup apparatus according to claim1, further comprising: a drive circuit which supplies a drive signal tothe drive wiring; a signal wiring, connected to a plurality of thetransfer switching elements in the column direction, for transmitting animage signal from the conversion element; and a signal processingcircuit which processes the image signal, and wherein the conversionelement is a MIS-type conversion element.
 9. A radiation image pickupapparatus comprising: a plurality of pixels arranged on a substrate inrow and column directions, each pixel having a conversion element whichhas first and second electrodes and converts radiation to an electricalsignal, and a transfer switching element which is connected to the firstelectrode of the conversion element and transfers the electrical signal;a first wiring connected to the second electrodes of the plurality ofthe conversion elements arranged in the row direction; a bias wiring forsupplying a bias voltage for operating the conversion elements; a resetwiring for supplying a reset voltage for a reset of the conversionelement; a bias switching element arranged between the bias wiring andthe first wiring; and a reset switching element arranged between thereset wiring and the first wiring, wherein at least the bias switchingelement and the reset switching element each comprise a poly-Si TFT. 10.The radiation image pickup apparatus according to claim 9, wherein thebias switching element comprises a first-type-channel TFT, the resetswitching element comprises a second-type-channel TFT, and thefirst-type channel is different type from the second-type channel. 11.The radiation image pickup apparatus according to claim 10, wherein thebias switching element comprises a P-channel TFT, and the resetswitching element comprises an N-channel TFT.
 12. The radiation imagepickup apparatus according to claim 9, wherein the conversion elementincludes: a wavelength converter which converts incident radiation tolight; and a photoelectric conversion element which converts the lightto the electrical signal.
 13. A radiation detecting system comprising:the radiation image pickup apparatus according to claim 9; processingmeans for performing image processing on a signal from the radiationimage pickup apparatus; recording means for recording a signal from theprocessing means; transfer means for transferring a signal from theprocessing means; and display means for displaying a signal from theprocessing means.
 14. A radiation detecting system according to claim13, further comprising: a radiation source which generates theradiation.